drawArrow method
Implementation
void drawArrow(Canvas canvas, Size size) {
canvas.drawLine(Offset(size.width / 2, size.height / 2),
Offset(size.width / 2 + 8, size.height / 2 - 10), _paint);
canvas.drawLine(Offset(size.width / 2, size.height / 2),
Offset(size.width / 2 - 8, size.height / 2 - 10), _paint);
}